1. Field of the Invention
The present invention relates to an ink jet printing device.
2. Description of the Related Art
Conventional ink jet printing devices, such as ink jet printers, include an ink jet head and a cap. The ink jet head includes a plurality of nozzles, a plurality of pressure chambers, common ink chambers, and an actuator. Each nozzle is open to outside the ink jet head. The pressure chambers are provided in a one-to-one correspondence with the nozzles and supply the nozzles with ink. The common ink chambers in turn supply all of the pressure chambers with ink through ink supply holes. The actuator includes a plurality of pressure generating portions in a one-to-one correspondence with the pressure chambers. The pressure generating portions apply pressure to the pressure chambers in order to eject ink from the pressure chambers. The cap is for abutting against the ink jet head so as to cover the nozzles.
The common ink chambers are positioned within a plane that is parallel with a plane defined by the plurality of pressure chambers. The common ink chambers are elongated in an alignment direction in which the pressure chambers are aligned and overlap with at least a portion of each pressure chamber in a direction perpendicular to the above-described plane. Each common ink chamber is shaped so that its cross-sectional area is substantially constant at all points in the alignment direction, that is, from the vicinity of the ink supply source to the farthest from the ink supply source.
However, when the common ink chambers are formed in this shape, air bubbles can easily become trapped at the end of the common ink chambers farthest from the ink supply source. These air bubbles can result in defective ejection of ink and can also obstruct refill of ink into the pressure chambers.
Japanese Patent Application Publication No. 2000-43253, for example, discloses an ink jet recording head with common ink chambers 120 with the shape shown in FIG. 1. As shown in FIG. 1, each common ink chamber 120 is shaped so that its cross-sectional area at a far-end side 121, which is the portion of the common ink chamber 120 that is farthest from an ink supply source 130, decreases at a fixed rate with distance from the ink supply source 130. This configuration helps discharge bubbles that accumulate at the far-end side 121.
However, when the common ink chamber 120 is shaped in this way, the strength of the ink chamber member 112, in which the common ink chambers 120 are formed, varies depending on the position in the alignment direction Dl of the nozzles 150. As a result, the ink chamber member 112 has different strength at different positions corresponding to different nozzles 150. For example, as shown in FIG. 2 the common ink chambers 120 have a larger cross-sectional area in a region A than in a region B. As a result, the ink chamber member 112 is weaker at the region A than at the region B.
As a result, the ink chamber member 112 more easily deforms at the weaker area in the region A, so that the pressure applied to the pressure chambers is partially absorbed by the region A. As a result, the pressure chambers that correspond to the region A have different ink ejection performance than the pressure chambers that correspond to the region B.
As shown in FIG. 1, a cap 810 is provided to cover the nozzles 150 of the ink jet head. When the cap 810 is in intimate contact with the ink jet head, the cap 810 is positioned not to overlap with the common ink chambers 120 in directions perpendicular to the plane defined by the common ink chambers 120. This positioning enables the ink jet head to withstand capping pressure from the cap 810.
However, this optimum positioning of the cap 810 is often not achieved for various reasons, for example because the common ink chambers 120 themselves can be shifted out of position by, for example, variations in assembly of the ink jet head. A capping margin C is designed into the ink jet head to take potential shift in position of the cap 810 into account. The capping margin C is secured by locating the common ink chambers 120 near the outer edges of the ink chamber member 112, away from the nozzles 150 in a direction D2 that is perpendicular to the alignment direction Dl. However, when the ink jet head needs to be quite small, it is often impossible to provide the capping margin C and at the same time secure sufficient volume for the common ink chambers 120.
It is an objective of the present invention to overcome the above-described problem and provide an ink jet print head capable of uniform ink ejection performance at all pressure chambers.
It is another objective of the present invention to provide an ink jet recording device with a small ink jet head that is also capable of securing sufficient volume for the common ink chambers.
In order to achieve the above and other objectives, there is provided an ink jet head including a cavity plate. The cavity plate is formed with a row of plurality of nozzles, a plurality of pressure chambers in one-to-one correspondence with the plurality of nozzles, a common chamber located between the nozzles and the pressure chambers, and a protrusion protruding into the common chamber. The common chamber distributes ink to the respective pressure chambers.
There is also provided an ink jet printer including the above ink jet head and a purging unit including a cap that covers over the row of the nozzles. The protrusion of the cavity plate serves as a support for the cap.
Further, there is also provided an ink jet head including a cavity plate. The cavity plate is formed with a row of a plurality of nozzles defining a first plane, a plurality of pressure chambers in one-to-one correspondence with the plurality of nozzles, a common chamber located between the row of the plurality of nozzles and the plurality of pressure chambers for distributing ink to the respective pressure chambers, an ink supply hole for introducing ink to the common chamber, and an open-space chamber. The common chamber defines a second plane parallel to the first plane. The ink supply hole introduces ink to the common chamber. The common chamber has an end portion with a smaller cross section with a distance from the ink supply hole. The open-space chamber is formed in adjacent to the end portion of the common chamber in the second plane defined by the common chamber.